Reel pipelaying vessels in the prior art have been generally of two types. The first of those utilizing a large horizontally disposed reel which is permanently mounted to a barge. A well-known pipelaying vessel of this type is known in the offshore industry as the "Chickasaw" which is described in the following patents, all of which are assigned to the assignee of the invention hereof:
Sugasti et al--U.S. Pat. No. 3,630,461 PA0 Gibson--U.S. Pat. No. 3,641,778 PA0 Mott et al--U.S. Pat. No. 3,680,432 PA0 Key et al--U.S. Pat. No. 3,712,100 PA0 Springett et al--U.S. Pat. No. 4,230,421 PA0 Uyeda--U.S. Pat. No. 4,269,540 PA0 Yenzer et al--U.S. Pat. No. 4,297,054 PA0 Springett et al--U.S. Pat. No. 4,340,322 PA0 Uyeda et al--U.S. Pat. No. 4,345,855
A second type of pipelaying vessel is a reel ship which has a particular hull construction to accomodate the support and operation of a vertically disposed reel. Such a reel ship has an advantage in being able to discharge pipe in deep waters where it is extremely difficult or impossible for horizontal reel barges to operate. This deep water laying capability is provided by an adjustable ramp assembly which mounts the pipe conditioning apparatus required for straightening and tensioning near the stern of the ship. Such ramp assemblies are adjustable to allow pipe to enter the water at very steep angles up to about 60.degree. while the horizontal reel barges are limited to about a 15.degree. entry angle.
A vertical reel dynamically positioned ship known as the "Apache" is well-known in the trade and is described in the following U.S. patents, all assigned to the assignee of the invention hereof:
The pipelaying vessels utilized in the offshore industry are capable of laying out pipelines with only prefabricated coatings thereon. Such coatings must be elastic and highly flexible since the pipeline is reeled onto the storage reels prior to layout. Such vessels have not been able to layout pipelines with relatively thick or inelastic coatings which can provide improved corrosion resistance, thermal insulation, dimensional integrity, and increased weight/unit length for the pipelines.
U.S. Pat. No. 3,599,435 describes but does not show a method for laying coated pipelines underwater involving a "stovepipe" layout. The coating of pipeline sections prior to the tensioning means only incurs the problem of fracturing the coating. This problem is some what alleviated by the solution set forth, but is not solved thereby. In this method there is no conditioning of the pipeline since there is no reel used. Coating prior to straightening would produce fractures in any coating layers deposited.
There are increasingly frequent requests in the offshore construction industry for the layout of pipelines having relatively thick walled coatings hereon.